Frequency synthesizers having dividing ratio controlled by sigma-delta modulator
First Claim
1. A frequency synthesizer comprising:
- detector means (110) responsive to a reference signal and a phase control signal (fd) for generating a control signal that varies in dependence upon the phase difference between said reference signal and said phase control signal;
means (118) responsive to said control signal for generating an output signal (fo) whose frequency varies in dependence upon said control signal;
means (106) for dividing said output signal (fo) to provide said phase control signal (fd), said dividing means having a control input and being operable to vary its division ratio in dependence upon a ratio control signal (b{t}) applied to said control input; and
second or higher order sigma-delta modulator means (102) responsive to a frequency control signal (δ
φ
) and to said phase control signal (fd) to provide said ratio control signal (b{t}), the sigma-delta modulator means (102) being arranged to displace any quantization noise in said ratio control signal (b{t}) away from the frequency of said phase control signal (fd) and multiples thereof.
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Accused Products
Abstract
An indirect frequency synthesizer suitable for use in a cellular radio system has finer resolution and reduced spurious frequencies and/or phase noise, which facilitates a large number of channels in a given bandwidth. The synthesizer comprises a phase detector responsive to a reference signal and a phase control signal for generating a control signal that varies in dependence upon the phase difference between the reference signal and the phase control signal. A voltage controlled oscillator responsive to the control signal generates an output signal whose frequency varies in dependence upon the control signal. A variable modulus divider divides the output signal to provide the phase control signal. The variable modulus divider varies its division ratio in dependence upon a ratio control signal derived by a second or higher order sigma-delta modulator in response to a frequency control signal δφ and to the phase control signal. The sigma-delta modulator displaces any quantization noise in the ratio control signal away from the frequency of the phase control signal and multiplies thereof. A direct frequency synthesizer may be implemented by means of the same sigma-delta modulator and variable modulus divider, but arranged so that the reference frequency signal is applied to the input of the divider, which divides it directly to provide the desired output frequency.
152 Citations
21 Claims
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1. A frequency synthesizer comprising:
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detector means (110) responsive to a reference signal and a phase control signal (fd) for generating a control signal that varies in dependence upon the phase difference between said reference signal and said phase control signal; means (118) responsive to said control signal for generating an output signal (fo) whose frequency varies in dependence upon said control signal; means (106) for dividing said output signal (fo) to provide said phase control signal (fd), said dividing means having a control input and being operable to vary its division ratio in dependence upon a ratio control signal (b{t}) applied to said control input; and second or higher order sigma-delta modulator means (102) responsive to a frequency control signal (δ
φ
) and to said phase control signal (fd) to provide said ratio control signal (b{t}), the sigma-delta modulator means (102) being arranged to displace any quantization noise in said ratio control signal (b{t}) away from the frequency of said phase control signal (fd) and multiples thereof. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A frequency synthesizer comprising variable modulus divider means (106) for dividing a reference signal (fr) having a predetermined frequency to provide an output signal (fod) of a desired frequency, the ratio of such division being variable in dependence upon a ratio control signal b(t), and second or higher order sigma-delta modulator means (102) responsive to a control signal (δ
- φ
) and to said output signal (fod) from said divider means (106) for supplying said ratio control signal b(t), the arrangement being such that any quantization noise in said ratio control signal b(t) is displaced away from the frequency of said output signal (fod) and multiples thereof. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
- φ
Specification